Method and apparatus for electrolytic material removal

ABSTRACT

Material is removed electrolytically from a conductive workpiece to form a cavity the peripheral edge of which is radiuses by first generating the cavity with a first stream of electrolyte charged cathodically with respect to the workpiece at an electrical potential sufficient to create in the electrolyte stream a condition at least of incipient glow. After generation of the peripheral edge, it is radiuses by contacting the edge with a second stream of electrolyte shaped generally to conform with the shape of the peripheral edge and charged cathodically with respect to the workpiece independently from the first stream. The second stream is charged in timed relationship with the first stream to control the radiusing action. The cathode tool used in such method includes a pair of electrodes electrically isolated one from the other and capable of being charged independently.

Oct. 9, 1973 5. EELLOWS 3,764,510

METHOD AND APPARATUS FOR ELECTROLYTIC MATERlAL. REMOVAL.

Filed April 19, 1972 2 Sheets-Sheet 1 G. BELLOWS METHOD AND APPARATUS FOR ELECTROLYTIC MATERIAL REMOVAL 2 Sheets-Sheet :3

Filed Apri] 19, 1972 ELEC Z OL fi United States Patent 3,764,510 METHOD AND APPARATUS FOR ELECTROLYTIC MATERIAL REMOVAL Guy Bellows, Cincinnati, Ohio, assignor to General Electric Company Filed Apr. 19, 1972, Ser. No. 245,374 Int. Cl. B01k 3/00, 3/04 US. Cl. 204-284 3 Claims ABSTRACT OF THE DISCLOSURE Material is removed electrolytically from a conductive workpiece to form a cavity the peripheral edge of which is radiused by first generating the cavity with a first stream of electrolyte charged cathodically with respect to the workpiece at an electrical potential sufiicient to create in the electrolyte stream a condition at least of incipient glow. After generation of the peripheral edge, it is radi used by contacting the edge with a second stream. of electrolyte shaped generally to conform with the shape of the peripheral edge and charged cathodically with respect to the workpiece independently from the first stream. The second stream is charged in timed relationship with the first stream to control the radiusing action.

The cathode tool used in such method includes a pair of electrodes electrically isolated one from the other and capable of being charged independently.

BACKGROUND OF THE INVENTION In the electrolytic generation of cavities in workpieces in which the cathode approaches the workpiece surface at an angle generally normal to or greater than about 70 to the surface, radiusing of the cavit will occur generally as a result of side current effects. However, when the angle of entry is below about 70", there is a substantial portion of the periphery of the cavity so generated which is not radiused.

In highly stressed applications of articles in which cavities are generated, it is desirable to radius the periphery of such cavities to reduce thermal and mechanical stress levels. Such radiusing results in greater life and longer structural integrity for the article. These radii also are desired to promote the smooth flow of fluids from or through such cavities.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide an improved method for electrolytically generating cavities, particularly small holes, in a workpiece, the method including radiusing of the periphery of the cavity after its generation and having multi-mode electrolytic capability.

Another object is to provide an improved cathode-tool for use in such method to provide separate charged and timed electrolyte streams, one for the generation of the cavit and another for the radiusing of the cavity periphery.

Still another object is to provide apparatus for use in such method and with such cathode-tool including means to supply electrical power independently to the two independent electrolyte streams and to control and time the application of such power.

These and other objects and advantages will be more clearly understood from the following detailed description, the drawings and the examples all of which are intended to be typical of rather than limiting on the scope of the present invention.

The method of the present invention, in one form, comprises producing in the workpiece a cavity having a pcripheral edge by removing material electrolytically from ice the workpiece. This is accomplished with a first electrolyte stream charged cathodically with respect to the workpiece at an electrical potential of at least about 50 volts and generally at least about 200 volts. The electrolyte is in a condition at least of incipient glow. After generation of the peripheral edge, the edge is radiused by contacting the edge with a second electrolyte stream generally shaped to conform with the peripheral edge shape and charged cathodically with respect to the workpiece. The second stream is charged in timed relationship with the first stream to enable cutting or radiusing action to be coordinated with cutting or hole drilling action.

The cathode-tool form of the present invention for use in such a method comprises inner and outer electrolyte guide members each having a hollow interior, an electrolyte inlet and an electrolyte discharge port. The inner member is smaller than the outer member and is located within the hollow interior of the outer member in spaced apart relationship to define therebetween an electrolyte passage. The electrolyte discharge ports of the members are adapted to discharge the electrolyte in substantially the same direction. Located within the electrolyte passage is a radiusing electrode and located within the hollow interior of the inner member is a cutting electrode. The two electrode systems are electrically isolated one from the other.

One such cathode-tool is used to practice the method of the present invention on apparatus for removing material electrolytically from a conductive workpiece. The apparatus includes means to supply electrical power, electrolyte supply means and means to hold the cathode-tool in opposed relationship with the workpiece. The means to supply electrical power supplies such power independently to the two electrode systems so that the electrodes are cathodic with respect to the workpiece. In addition, the apparatus includes control means which, among other functions, enables the scheduling of the supply of electrical power to the electrodes so that the radiusing electrode is activated independently of and in timed relationship with the cutting electrode. Such control means also coordinates the flow of electrolyte and relative movement between the cathode-tool and the workpiece with the supply of electrical power.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged fragmentary sectional view of the cathode-tool of the present invention practicing the method of the present invention; and

FIG. 2 is a diagrammatic view of the apparatus of the present invention used in the practice of the method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is particularly useful in connection with the electrolytic generation of small holes through a metallic workpiece. Therefore, the invention will be described in connection with such application. However, it should be understood that this description of the preferred embodiment is not intended to limit the scope of the present invention. While cavity or hole drilling is described in detail, the present invention includes within its scope the application of dual or multiple electrolytic techniques when applied sequentially during the stroke of the machine regardless of the shape being generated.

Ordinary electrolytic material removal, sometimes referred to as electro-chemical machining or electro-chemical drilling and which follows the rules of normal electrolysis, is conducted with a cathodic tool spaced from an anodic workpiece across a relatively narrow electrolyte filled gap. Because of the proximity of the electrodes in such a cell arrangement, ordinarily only a relatively low electricalpotential, for example, less than about 20 volts, is required through the electrolyte to bring about electrolytic material removal or deplating from the anodic workpiece. In such ordinary methods, cathodes have been used in the shape of relatively small tubes, the exposed working surface of which is very small where it faces the workpiece. Also used have been relatively large cathode-tools having a working surface relatively large and complex in contour for cooperation with the workpiece from which it removes relatively large amounts of material forming cavities or holes.

The present invention, however, relates for principal cavity generation to that kind of material removal process described in US. Pat. 3,403,084Andrews, issued Sept. 24, 1968 and assigned to the assignee of the present invention. In such improved process, greater amounts of material can be removed electrolytically than can be anticipated from Faradays Law. This results from the unusual condition created in a charged electrolyte stream contacting both the cathode and the workpiece across a gap significantly greater than that used in normal electrolysis. In order to achieve such enhanced material removal, the condition in such electrolyte stream is adjusted through the application of relatively high voltage for electrolytic material removal to create a condition at least of incipient glow. Under such a condition, the current begins to decrease with increasing voltage rather than increase as is the case in normal electrolysis. This is reported by Kellogg in the Journal of Electrochemical Society 1950, 97, 133-142. Therefore, this transition region is sometimes referred to as the Kellogg Region. The voltage required will vary depending upon the gap between the cathode and the workpiece; an electrical potential as low as 50 volts has been used successfully although generally at least about 200 volts is required for practical applications.

The method of the present invention generates a cavity electrolytically in a workpiece according to the Andrews method, such cavity having a relatively sharp peripheral edge. If the angle of attack of the charged electrolyte stream toward the workpiece surface is substantially normal to such surface, there generally will be sufiicient side current effects to radius the peripheral edge. However, when the angle of attack is less than about 70, substantial portions of the peripheral edge are undesirably sharp so as to create stress-riser conditions. Thus, it is required that they be radiused for high stress operation. However, separate radiusing operations are time consuming and costly. Practice on the present invention allows the generation of the cavity or hole and the radiusing of the peripheral edge in the same set up or tooling arrangement.

One form of the cathode-tool of the present invention is shown generally at in FIG. 1. An outer hollow electrolyte guide member 12 sourrounds an inner hollow electrolyte guide member 14. The inner guide member is smaller than and is located within the hollow interior of the outer guide member, in spaced apart relationship to define therebetween an electrolyte passage 16. Each guide member has an electrolyte inlet, 18 for the outer guide member and 20 for the inner guide member. In addition, each guide member has an electrolyte discharge port, 22 for the outer guide member and 24 for the inner guide member. The electrolyte discharge ports are located in the assembly which defines the cathode-tool of the present invention, so as to discharge electrolyte in substantially the same direction from the hollow interiors.

Located within electrolyte passage 16 is a radiusing electrode 26. Such an electrode can be provided within passage 16 in a variety of forms, for example, as a tube, as a conductive coating, as a plurality of wires or rods, etc. A cutting electrode 28 is located within the hollow interior 30 of the inner guide member 14. The two electrode systems, 26 and 28 respectively, are electrically isolated one from the other to enable separate scheduling or timing of the application of electrical potential between such electrodes and the workpiece by control means 38 shown in FIG. 2. The timing generally first brings about application of potential from higher electrical power supply 44 through conductor 48, to cutting electrode 28 to initiate production of the principal cavity, thereby creating a peripheral edge about the cavity. Then lower potential is applied to radiusing electrode 26 from lower electrical power supply 46 through conductor 50 to initiate radiusing action when electrode 26 is in a desired position in respect to the workpiece. Because the scope of the present invention includues multi-Inode operation, the electrolyte between electrode 26 and the peripheral edge can be either in a normal electrolysis condition under which ordinary electrolytic removal occurs or it can be in a condition at least of incipient glow under which enhanced removal occurs. Potential to radiusing electrode 26 can be applied from power supply 46 either during or after operation of cutting electrode 28.

Control means 38 includes, in addition to the capability of such scheduling of the application of electrical potential from power supply means 44 and 46, the capability of controlling and timing the flow of electrolyte through the cathode-tool and the relative movement between the cathode-tool and the workpiece. Control means 38 is comprised of ordinary switching, sensing and other scheduling components normally used in the art and commercially available.

Apparatus which incorporates the cathode-tool of FIG. 1 in the practice of the method of the present invention is shown diagrammatically in FIG. 2. The cathode-tool shown generally at 10 is held in opposed relationship with a workpiece 32 in which a cavity or hole is being generated electrolytically through contact with a stream of cathodically charged electrolyte 34 directed from inner guide member 14 toward and in contact with anodic workpiece 32.

In the operation of the method of the present invention, in one form, the cathode-tool, which is held by a tool holding and locating means shown generally at 36, is positioned over and directed toward an anodic workpiece at the point at which such hole is to be generated. As indicated diagrammatically in FIG. 2, tool holding and locating means 36 is capable of three dimensional movement to advance, retract or otherwise position the cathode-tool as desired. Such a movement, which is coordinated with the flow of electrolyte and the application of electrical potnetial, is scheduled and controlled by control means 38.

As was mentioned before, the first stream of cathodically charged electrolyte 34 directed from the interior 30 of inner guide member 14 is in the so called Kellogg Region or in a condition at least of incipient glow. Therefore, it is necessary that the walls of such guide member be dielectric. As that term is used herein, it is intended to include electrical isolation from the electrodes, from the streams of electrolyte and from the workpiece. In addition, it is preferable, as shown in the drawing, that the outer electrolyte guide member 12 be dielectric as well. However, the condition of the second stream of cathodically charged electrolyte 42 need not be in the Kellogg Region, nor at least at incipient glow, in order to accomplish radiusing action, according to the multi-mode capability of the present invention.

After the hole has been generated to a desired depth, or through the entire workpiece as shown in FIG. 1, control means 38 applies electric potential from power source 46 to activate the radiusing electrode 26. Also, control means 38 can initiate flow of electrolyte through passage 16, if it has not previously been flowing, to form second charged electrolyte stream 42 which initiates electrolytic radiusing action at the peripheral edge 40 of the hole generated. Such second electrolyte stream 42 preferably is shaped to conform generally with peripheral edge 40. It should be understood that such radiusing action is controlled by the application of potential between electrode 26 and the workpiece, not necessarily by the flow of electrolyte through passage 16. Such flow can exist without activation of electrode 26.

Such radiusing action can occur while the cutting electrode 28 is still in operation, for example, to complete the lower portion of the hole generated. Alternatively, it can be scheduled to begin after the hole has been completed and after termination of the electrical potential or the feed motion or both between cutting electrode 28 and the workpiece 32, and after termination of the flow of electrolyte through the hollow interior 30 of the inner guide member.

At initiation of the radiusing portion of the operation, control means 38 activates fiow of electrolyte into electrolyte passage 16 and activates radiusing electrode 26 to charge second stream of electrolyte 42 cathodically with respect to workpiece 32. The radiusing electrode 26 is shown to be positioned somewhat remote from the workpiece. However, because it is not necessary that the second stream 42 of cathodically charged electrolyte be at incipient glow, such radiusing electrode can be positioned more closely to workpiece 32. Under such conditions, the radiusing operation is in the normal electrolytical material removal manner across a relatively narrow electrolytic machining gap.

Thus, there is provided, through the present invention, improved apparatus including an improved cathode-tool which performs a method of radiusing the periphery of an electrolytically generated hole without the need for additional tooling or repositioning of the workpiece or tooling.

What is claimed is:

1. For use in electrolytic material removal, a cathodetool comprising:

inner and outer electrolyte guide members, each havingwalls defining a hollow interior, an electrolyte inlet and an electrolyte discharge port;

the inner member being smaller than the outer member, having dielectric walls and located within the hollow interior of the outer member in spaced apart relationship to define therebetween an electrolyte passage;

the electrolyte discharge ports of the members being located to discharge electrolyte in substantially the same direction;

the electrolyte discharge port of the outer guide member being spaced apart from the electrolyte discharge port of the inner guide member axially of the cathodetool and toward the electrolyte inlets;

a radiusing electrode in the electrolyte passage and distinct from the guide members; and

a cutting electrode in the hollow interior of the inner member and distinct from the guide members;

the radiusing and cutting electrodes being electrically isolated one from the other.

2. The cathode of claim 1 in which the inner and outer electrolyte guide members are tubular.

3. The cathode-tool of claim 1 in which the inner and outer guide members are located concentrically.

References Cited UNITED STATES PATENTS 3,293,166 12/ 1966 Cowing 204 3,352,770 11/1967 Crawford et al. 204 3,075,903 1/ 1963 Costa et al. 204-429.6 3,403,084- 9/1968 Andrews 204 3,468,784- 9/1969 Joyce et al. 204

JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 204-272 

